Various photosensitive materials have been proposed to date for use in an electrophotographic photoreceptor. With respect to a laminate type electrophotographic photoreceptor whose photosensitive layer is composed of a charge generating layer and a charge transporting layer, various organic compounds have been reported as a charge generating material.
Recently, there has been an increasing demand to extend the photosensitive wavelength region of conventional organic photoconductive materials to a longer side (780 to 830 nm) which corresponds to a wavelength region of a semiconductor laser of near infrared light so as to make them applicable to digital recording using a laser printer, etc. From this point of view, there have been reported photoconductive materials for semiconductor lasers, such as squarylium compounds as disclosed in JP-A-49-105536 and JP-A-58-21416, triphenylamine type trisazo compounds as disclosed in JP-A-61-151659, and phthalocyanine compounds as disclosed in JP-A-48-34189 and JP=A-57-148745 (the term "JP-A" as used herein means an "unexamined published Japanese patent application").
In cases where an organic photoconductive material is used as a photosensitive material for semiconductor lasers, they are required to have a photosensitive wavelength region extended to a longer side and to provide a photoreceptor having satisfactory sensitivity and durability. None of the above-described conventional organic photoconductive materials sufficiently satisfies these requirements.
In order to overcome the drawbacks of the conventional organic photoconductive materials, the relationship between their crystal form and electrophotographic characteristics has been studied. In particular, many reports have been made on phthalocyanine compounds.
It is known that phthalocyanine compounds generally exhibit several different crystal forms depending on the process of production or the process of treatment and that the difference in crystal form has a great influence on their photoelectric conversion characteristics. For example, known crystal forms of copper phthalocyanine compounds include .alpha.-, .epsilon.-, .pi.-, .chi.-, .rho.-, .gamma.-, and .delta.-forms as well as a stable .beta.-form. These crystal forms are known to be capable of interconversion by a mechanical strain, a sulfuric acid treatment, an organic solvent treatment, a heat treatment, and the like as described, e.g., in U.S. Pat. Nos. 2,770,629, 3,160,635, 3,708,292, and 3,357,989. Further, referring to a relationship between the crystal form of copper phthalocyanine and electrophotographic sensitivity, JP-A-50-38543 states that an .epsilon.-form has higher sensitivity than any of .alpha.-, .beta.-, and .gamma.-forms.
Various crystal forms have been proposed, too, with respect to titanyl phthalocyanine (oxytitanium phthalocyanine). Examples of such crystal forms of titanyl phthalocyanine and electrophotographic photoreceptors using them are described in JP-A-62-67094, JP-A-63-365, and JP-A-64-17066.
However, any of the known phthalocyanine compounds proposed to date is still unsatisfactory in photosensitivity and durability when used as a photosensitive material. It has thus been demanded to develop a phthalocyanine compound of new crystal form.